<?php
function randomColor() {
    $str = '#';
    for($i = 0 ; $i < 6 ; $i++) {
        $randNum = rand(0 , 15);
        switch ($randNum) {
            case 10: $randNum = 'A'; break;
            case 11: $randNum = 'B'; break;
            case 12: $randNum = 'C'; break;
            case 13: $randNum = 'D'; break;
            case 14: $randNum = 'E'; break;
            case 15: $randNum = 'F'; break;
        }
        $str .= $randNum;
    }
    return $str;
}
$color = randomColor();